1. Field of the Invention
This invention relates to pelletized carbon black having enhanced dispersion properties.
Carbon black became widely used for reinforcement of rubber in the early 1920's. At that time it was packaged in cartons or drums because it was a light and dusty powder. Shipping and storage were costly due to the low density. Mixing into rubber was difficult.
An improvement in packaging, shipping and storage was obtained with the introduction in the early 1930's of the dry process for pelletizing carbon black. Dry process pelletized carbon black is easier to mix into rubber than powder. However, the pellet is very fragile causing fines and dust problems with the handling of this material.
Wet process pelletized carbon black, introduced in the 1940's, has bulk handling properties superior to dry process carbon black. However, an inherent deficiency exists with all wet process pellets due, in part, to the method itself. In the initial stage of the process the carbon black powder is wetted and densified by agitation in an appropriate apparatus. In the final stage the pellet is coated-out or layered with dry powder that has not been properly densified. As a result, wet process pellets have an exterior that is easily attrited into fines. This causes problems with bulk shipping and with mixing into rubber. Attempts to improve the surface attrition with thermosetting binders, such as molasses, usually produce pellets having interiors that are hard to disperse in soft polymers. All conventional pelletizing processes in commercial use today produce carbon black pellets by bonding aggregates into agglomerates. The bonding mechanism is thought to include both chemical and physical forces. These forces develop when clean surfaces of two aggregates touch. The bonding strength is sufficient to prevent complete deagglomeration by normal rubber mixing methods.
2. The Prior Art
U.S. Pat. No. 3,565,658 describes use of polyethoxylated amines both as a pelletizing agent and a dispersing agent for carbon black.
U.S. Pat. No. 3,282,713 describes an oleaginous pelletizing material for carbon black.
U.S. Pat. No. 4,102,967 describes a pelletizing process using a carbohydrate and a hydrocarbon oil or oil emulsion to produce dust-free carbon black pellets.
Many additional additives and processes have been described in the art, but there has been a continuing need for a carbon black product which is easily produced, stable, non-toxic and easily dispersed in an elastomer. Such a product is provided by the present invention.